1. Field of the Invention
The field of the present invention is acoustic and electromagnetic beam formation, and more particularly, phase shift beamformers for transducer arrays operating on narrow-band signals.
2. Description of the Prior Art
It is known that electromagnetic antennas or acoustic hydrophone arrays may be steered by phase shift systems. U.S. Pat. No. 3,002,188 discloses a beam steering system comprising two transformer elements coupled to each transducer element to split the transducer output into two components, one having an amplitude proportional to the cosine of the phase shift to be introduced, the other having an amplitude proportional to the sine of the phase shift. The respective cosine and sine components of all of the array elements may then be coherently summed to form composite component values, each substantially equal in power to the power induced in one of the transducer elements times 1/2 the number of elements. These two signals are phase shifted by 90.degree. relative to each other and passed through a summation network to yield an output signal whose power is substantially equal to the power induced in any one transducer in the array times the number of transducers. An alternate embodiment utilizes a discrete capacitive matrix to realize the desired proportionalities in the sine and cosine components.
While the system disclosed in U.S. Pat. No. 3,002,188 operates in a satisfactory manner, it has certain drawbacks. For example, the transformer (or discrete capacitive matrix) network is quite bulky and relatively expensive to fabricate, and the accuracies of the element gains and phases are somewhat limited. These drawbacks are to some extent addressed by utilizing a resistive element phase compensator system such as is described, for example, in the Navy Electronics Laboratory Report 1148, "Simultaneous Multibeam Phase Compensation: X1, A Resistive-Element Phase Compensator," by L. D. Morgan and R. D. Strait, Dec. 4, 1962. However, even the resistive-element systems require a significant number of discrete elements, so that the beam steering system is still quite bulky. Moreover, the accuracies of the component gains and phases are still limited.
Unrelated to phase-shift beamformers, there has been extensive recent application of switched capacitors to LSI filters. Two examples of papers discussing the subject are "MOS Switched-Capacitor Filters," by R. W. Broderson, P. R. Gray and D. A. Hodges, Proceedings of the IEEE, Vol. 67, No. 1, January 1979, pp. 61-75, and "Applications of CCD and Switched Capacitor Filter Technology," by C. R. Hewes, R. W. Broderson and D. D. Buss, Proceedings of the IEEE, Vol. 67, No. 10, October 1979, pp. 1403-1415.
It is an object of the present invention to provide a phase shift beam steering system which achieves substantial reduction in required hardware over previous systems.
It is another object of the present invention to provide a beam steering system which may be fabricated on LSI chips.
A further object of the invention is to provide a phase shift beamformer whose respective phase shifts may be realized to a high degree of accuracy.
It is yet another object of the present invention to provide a beam steering system wherein the proportionality between signal components is achieved by utilization of switched capacitors.
Another object of the invention is to provide a beam steering system wherein the respective signal component ratios remain substantially constant over a wide range of system operating conditions.